RF transmitters are electronic devices comprising an oscillator, modulator, and other components and circuits, which are adapted to produce a radio frequency signal. A RF transmitter comprises a plurality of stages, in which each stage is adapted to modify a signal so as to produce a desired output. In a first stage, for example, an oscillator may be adapted to generate a desired operating frequency. The output from this first stage is then amplified to a desired transmitter output value by a power amplifier.
The evolution from wireless based voice only communication networks to wireless based voice and data communication networks has resulted in the development of general packet radio service (GPRS) and enhanced data rates for the global system for mobile communications (GSM) standards. Although speech still remains the dominant service by many cellular service providers, existing systems are being upgraded to provide greater support for data communication via the radio interface.
The GSM standard, for example, provides data services with bit rates up to 14.4 kbps for circuit-switched data and up to 22.8 kbps for packet based (non-circuit switched) data. For GSM, higher bit rates may be achieved utilizing technological advancements such as high-speed circuit-switched data (HSCSD) technology and general packet radio service (GPRS) technology, which are based on the original gaussian minimum shift keying (GMSK) modulation scheme employed by GSM. In eight-state phase shift keying (8PSK), there are eight possible states that a signal can transition to at any time. 8PSK is a variation of PSK and has a symbol rate that is one third of the bit rate. Minimum Shift Keying (MSK) is used in the GSM cellular standard. Frequency Shift Keying (FSK) and MSK produce constant envelope carrier signals, which have no amplitude variations, a desirable characteristic for improving power efficiency of transmitters. In practice, waveforms are filtered with a gaussian filter, resulting in a narrow spectrum and no time domain overshoot. MSK with a gaussian filter is termed GMSK. GMSK is a spectrally efficient modulation scheme and is useful in mobile radio systems. GMSK has a constant envelope, spectral efficiency, good bit error rate (BER) performance, and is self-synchronizing.
Enhanced data for global evolution (EDGE) provides an enhancement to GPRS, which leverages a new modulation scheme along with various coding and radio link enhancements to provide much higher bit rates and capacity than GPRS. Due to the higher bit rates and the need to adapt the data protection to the channel and link quality, the EDGE radio link control (RLC) protocol is somewhat different from the corresponding GPRS protocol. EDGE is a 3G technology that delivers broadband-like data speeds to mobile devices. It allows consumers to connect to the Internet and to send and receive data, including digital images, web pages and photographs, three times faster than possible with an ordinary GSM and or GPRS networks. EDGE enables GSM operators to offer higher-speed mobile-data access, serve more mobile-data customers, and free up GSM network capacity to accommodate additional voice traffic.
As the operating requirements for wireless devices become more demanding, the complexity of the interactions between data processing hardware and RF transmitters also increases. For example, RF transmitters from various vendors may be required to work effectively with a baseband processor from a different vendor. The use of individual baseband transmitter interfaces for each of the possible RF transmitters with which a baseband processor may interface, may prove to be costly in terms of layout space in an integrated circuit. Because component size and cost are critical concerns in wireless devices, the use of multiple baseband transmitter interfaces should be limited as much as possible. Moreover, this approach may also limit the number of possible interfaces that may be implemented with a particular baseband processor.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.